The present invention relates to a method for manufacturing a glass sheet having an uneven surface. The present invention also relates to a method for manufacturing a glass sheet having an uneven surface on one side, and a thin film formed on the other side.
In the method for manufacturing glass sheets known as the xe2x80x9cfloat methodxe2x80x9d, first, raw glass material that has been melted in a tank furnace (float furnace) is transferred to a tin bath. When the molten glass material is transferred to the float bath, it spreads over the tin, whose specific weight is larger than that of the glass, and forms a glass ribbon. The thickness of the glass ribbon is adjusted while the glass ribbon advances inside the float bath, and it is cooled so that it has a viscosity with which it can be retrieved from the bath. The cooled glass ribbon is lifted out of the float bath and conveyed into an annealing lehr, where it is annealed, and subsequently cut into glass sheets of predetermined size. The float method is widely used for low-cost mass production of glass sheets having a pair of smooth and parallel surfaces.
One way of reducing reflections on the glass surface is to make the glass surface rough. Usually, such a glass sheet is obtained by physically or chemically processing the smooth surfaces achieved with the float method. A physical method is, for example, sand-blasting, whereas etching with hydrofluoric acid is one of the known chemical methods. These methods are typically applied to the glass sheet obtained by cutting the glass ribbon, and are usually performed in a production line that is separate from the glass sheet production line (i.e. as offline processing).
Aside from the float method, rolling out molten glass with a pair of (upper and lower) rollers is widely used as a method for manufacturing patterned glass sheets or wire glass sheets for buildings. In this manufacturing method, the pattern (i.e. the unevenness of the surface) of the patterned glass is formed by continuously transferring a pattern carved in one of the rollers, without necessitating offline processing.
As one of the manufacturing methods using rollers, JP 57-178514 B discloses a method of conveying a glass ribbon that has been rolled out with rollers over molten tin. In this method, the molten tin supports the rolled out glass sheet, so that the portions that locally have become thinner where a pattern has been formed do not droop below the other portions.
Thus, conventional methods for manufacturing glass sheets having an uneven surface include the method of rolling out the glass sheet with rollers and the method of offline processing glass sheets made with the float method. However, in the former method, there is a limit to the thickness of the glass sheet that can be produced. Moreover, because the surface is formed by rolling with rollers, it is not possible to make one surface uneven while maintaining a superior smoothness of the other surface. For the latter method, offline processing leads to the problem of a lower production efficiency.
It is therefore an object of the present invention to provide a method for efficiently manufacturing a glass sheet having an uneven surface, using a technique for processing the surface of a glass sheet that is suitable for a production line for float glass.
In order to achieve this object, a first inventive method for manufacturing a glass sheet with the float method by forming molten raw glass material on a metal bath into a glass ribbon includes making a surface of the glass ribbon facing the metal bath uneven by bringing the surface into contact with bubbles generated inside the metal bath.
In this first method, it is preferable that the bubbles are brought into contact with the glass ribbon where the viscosity of the glass ribbon is between 103 and 106 poise.
To achieve the above-noted object, a second inventive method for manufacturing a glass sheet with the float method by forming molten raw glass material on a metal bath into a glass ribbon includes making a surface of the glass ribbon facing the metal bath uneven by bringing the surface into contact with a roller arranged downstream from the metal bath in a conveyance direction of the glass ribbon.
In this second method, it is preferable that the surface is made uneven by contacting the roller with the glass ribbon where the viscosity of the glass ribbon is between 107 and 1013 poise.
The present invention makes it possible to manufacture glass sheets having an uneven surface efficiently. Moreover, the even surface can have an excellent surface smoothness.
The present invention also provides a method for manufacturing a glass sheet having an uneven surface on one side and a thin film formed on the surface of the other side. This method can be easily integrated into a production line for float glass, and does not necessitate offline processing. More specifically, this method includes making the surface of the glass ribbon facing the metal bath in the first or the second method uneven, and forming a thin film on a surface of the glass ribbon facing away from the metal bath. There is no particular limitation to the order of making the surface uneven, and forming the thin film, as long as these operations are integrated into the same production line. Moreover, it is also possible to combine the first method and the second method to make the surface uneven.